Morrison's diesel (again!)

I stopped using it years ago, my old van did thirty less miles to a tank on Morrison’s compared to my local Jet, this was when I was driving the same 150 mile journey nearly every day for nine months, the Jet garage is near my house, and the Morrison’s was next to my destination, so I was using nearly two tank fulls a week. Same result every time.

It's more likely the hot weather use of the A/C and possibly more traffic on the roads

My son is a service advisor in a dealership in Norfolk and he has told me repeatedly how many cars they've had in with problems all relating to Morrisons fuel so apparently it's well known in the trade.

I had something similar happen to my car a few months ago.
Filled up (about 50 litres) at Morrisons rather than at my usual (other supermarket brand) staition and within 50 miles I notciced a drop of 6-8mpg on the trip computer. This was confirmed by me needing to fill-up about 70 miles earlier than usual. (During that time the car was only used for commuting along the same route I've used for years)
When I filled up again, at my usual place, mpg when back up to usual level within about 60-70 miles.

I know there's lots of circumstantial evidence about Morrison's diesel out there, but I don't buy it. The diesel they sell conforms to EN590 standards, that's all that matters really (unless you're in a lab).

I know air-conditioning was on both ways but in hotter weather it will draw far more power. Cooling fan may well have been on too, even the coefficient of friction with the road could change significantly with a change of temperature.

I work in diesel engine development with customers that are very picky about economy, for good reason. My job involves interpreting results from field test vehicles around the world and differences in fuel economy Vs expectation can have lots of explanations, like the ones I've given above. I've seen lots but never seen fuel be the issue

Edited for typo

Sorry Benrad. Fully understand what you are saying and respect your profession but no. I have driven my car over 100k miles and in hotter weather than this week. AC has been on before and no noticable difference in economy. Car was on constant motorway driving which generates air flow as you are probably aware. Have only ever had the fan on a few times and that was in a traffic jam. My temp gauge never moves and although the car probably could do with a coolant flush you have missed one piece of evidence being it was fine before I filled up. Just to add another piece of info... I actually turned the AC off, reset my trip and still crap MPG. So no. However and not wishing to dismiss your experience, maybe looking at Morrison's diesel and it's effects is a good project for you? No point in spending hours looking a the effects of increased rust coefficients due to heat if there is crap fuel in circulation which is killing the economy of your customers and then sell your findings to Morrison's.

Auto810graphy. Like the other emerging posts there seems to quite a bit of anecdotal evidence to support that Morrison's fuel delivers less mpg. Haven't seen anything scientific yet to suggest anything different.

Of course it could be just a coincidence and at the exact same time I filled up and reset my trip computer something wore out/broke. Eg. Exhaust manifold which is common. (have taken cover off and checked this and.... No!. Air filter 1000 miles old. No. Replaced fuel filter at same time at expense of my knuckles so... No).

I hate spending money of fuel as filling up doubles the value of my car. But can't wait this time!

This is a easy one to answer - they can put biodiseal and/or ethanol in petrol/diesal. these have less calories than petrol/diesal so more is used = more fuel compsumption for the same distance = lower mpg.

I had a merc vito with the v6 cdi that had a penchance for dying into limp mode at me with no explanation every few months or so for the 12 years I drove it... Only fairly consistent provoker seemed to be supermarket fuel, and Morrison's was the one nearest me.

Why would Morissons be interested? They sell more fuel as a result.

Do you know what was causing limp mode, what error codes it had?

Obvious ones would be blocked fuel filter (low fuel pressure world be the code), but that would only be fixed by changing the filter, not changing the fuel. Or water in fuel, which would normally need you to drain the filter. Unlikely to be one thing about the fuel that could cause both poor fuel economy and limp mode. If you know the error codes that might point in a certain direction though